She knew it would turn out like this.
He did, too. That's why he'd stuck around when everyone else had heeded the warnings, and laughed with her instead of leaving her. He'd smiled and they'd made light of it, joking and pretending that there was a chance she'd control it long enough to matter.
For a little bit, she thought she'd started to believe she would.
It was such a nice fantasy to believe, after all. It wasn't as if she'd wanted to die, it certainly wasn't that she wanted to hurt anyone, either. She'd chosen to take the unstable seal and hold the beast at bay for a little while (on a flimsy promise that a master of seals would get there eventually) because she couldn't bear to allow anyone else to take it. She volunteered before anyone else could just to protect them, of course she didn't want to hurt them.
She didn't want to hurt Kakashi, either, so when he stated in no uncertain terms that he refused to leave, that he would be the one to stop her and no one else if it was necessary, it was happier to think that with his help and a confident spirit she could make it until the seal master arrived.
They both knew it would never work out that way. Not everyone was meant to be a Jinchuuriki, and not everyone could handle the beasts even with proper seals. With the slipshod, barely strung together chains around the Five Tails, even the best Jinchuuriki (maybe not the best Jinchuuriki, they had sealing magic of their own) would have eventually lost to the stampeding beast.
Before it happened, she could feel her consciousness straining, waning as the hoofbeat in her mind steadily drowned out her heartbeat.
He could see it, too. It must have been in her eyes, the strain and the loss of focus. She knew she was losing the moment his easy smile faded away into a look of grim expectation: a look of quiet sadness.
She didn't know what to say. She didn't know what a person was supposed to say in a situation like this, what was expected of her or what could be said in the time that she had left. She knew she was supposed to be spending her effort and her remaining consciousness on keeping it under control to give him and the other villagers more time to get away…but she knew he wouldn't.
Apologies slipped free.
I'm so sorry
Sensei
She wanted him to flee like the others, she wanted him to stop her, maybe to save her, but she was old enough to know no one could do that. Not even the man with a thousand jutsu.
Despite the fact that she was the one apologizing, and she was the one failing, his expression didn't show forgiveness or sympathy or sadness or pity.
As her vision burned away in the fiery chakra of the emerging beast, his expression darkened over with guilt.
She wondered, in the moments she had in darkness, for the brief time her body could hold out with the transformation and escape of the tailed beast, whether his guilt was because he couldn't save her
or whether it was because he couldn't stop her.